|Image from Unsplash by Todd Pham|
Humans with the ability to shrink have been a common feature of sci-fi and superhero fantasies for ages. (I say sci-fi rather than science fiction, because of the dilemma I'm about address.) We've had The Incredible Shrinking Man (probably the best of the bunch), Fantastic Voyage, Honey I Shrunk the Whatever, Ant Man and more. But while I accept that SF has to be flexible about the science, in the tradition of Larry Niven's 1969 essay Man of Steel, Woman of Kleenex, I feel we ought to at least consider the problems that arise from human shrinkage.
There seem to be two possibilities open to a would-be human miniaturiser. Either the reduced-size human temporarily misplaces the vast majority of their atoms, or they undergo some sort of process whereby the amount of empty space in atoms is reduced, so they still contain all the matter that they had previously, but in a compacted form.
Neither is particularly practical, but science fiction doesn't have to worry about this - faster than light travel is no picnic in the real world. But of the two possibilities, the atom compaction seems the more likely method because it's a far simpler concept. And I suspect for most sci-fi examples this is what the writers have in mind. However, there's a big problem for that image I conjured above of the tiny person being carried by someone in a plastic bag. Compacting would not reduce mass. The tiny person would have the same mass (and weight) as they always had, rather in the same way that a neutron star or a black hole retains its mass in a much smaller form.
This doesn't just make carrying the miniature being in the way usually demonstrated impossible. It would mean that their tiny feet exerted far more pressure than was normally the case. Pressure depends on surface area. Say the person reduced in height from 170cm to 5cm. That's a linear reduction of 34x, so the surface area reduction would be 1,156 times - and as the pressure produced by a person is simply a function of weight over surface area, that means the pressure exerted by the feet would go up by a factor of 1,156. It's not uncommon in shrinking movies for characters to be chased through grass much higher than their head by insects or spiders. But with so much more pressure on the feet, the collapsed individual would simply disappear deep into the soil.
If we think, then, of what miniature characters get up to, it's probably better to go for a corresponding reduction in mass. Mass decreases with volume - so the cube of the linear reduction. My 34x shrunken person would reduce from, say, 170kg to less than 5 grams. That's light - think about the weight of a sheet of A4 paper, a 20p piece or a US nickel. Easily carried. No pressure problems. But there are two issues.
One is just making it happen. As I mentioned above, it's relatively easy to imagine there could be some mechanism to shrink every atom, even if there isn't a genuine physical means to do it. But what we have to do here is remove 39,303 out of every 39,304 atoms in the body, nice and evenly. We then have to store them somewhere - imagine a big bag of gloppy atoms under the bed, perhaps. And we have to reinsert them when required, all in the right places, or we'd end up with something like the disastrous transporter scene in Galaxy Quest.
But even if the practicalities could be overcome there is a significant issue for our mini-people. They will be left with 0.0025 per cent of the cells in their brain. A human brain weighs about 1,350 grams on average. The typical shrunken brain would weigh 0.034 grams. Compare this with, say, a hamster's brain at 1.4 grams. Of course, weight isn't everything. Something human brains have an awful lot of is neurons, with somewhere around 16 billion in the cerebral cortex. The tiny person would be left with about 400,000. That still sounds a lot. But bear in mind a mouse has about 13 million.
Although there is no perfect measure of brain size/neuronal count that corresponds to intelligence, there can be little doubt that a human miniaturised by atom-loss would also be significantly less intelligent than a mouse or hamster. So the chances of shrinking down and saving the world are pretty slight.
Am I breaking a butterfly on the wheel? Quite possibly. But it's fun, isn't it?